Dumb engine harness wire question.

[Rdchallenger]

What does this long wire and connection go to? Lol

[anlauto]

Looks like the brake warning light, but that should be in the headlight harness 

[Rdchallenger]

Interesting... Here's the end of the connection

[Skid Row]

  Should go to the proportioning valve I believe.

[Rdchallenger]

Should go to the proportioning valve I believe.

I was thinking that, especially after Alan said what it may be as well. That's one hell of a long wire to go right to the proportioning valve.
Thanks for the help guys!